The present invention relates generally to image-guided navigation. More particularly, the present invention relates to methods and systems that employ a technique for determining a navigated point that uses an image-plane constraint to reduce navigation errors.
Image-guided navigation systems typically include an imaging system and an electromagnetic tracker and have been used to provide an operator (e.g., a physician) with information to assist in the precise and rapid positioning of a medical (e.g., surgical) device in a patient's body. In general, an image may be displayed for the operator that includes a visualization of the patient's anatomy with an icon or image representing the device location projected thereon. As the device is positioned with respect to the patient's body, the displayed image may be updated to reflect the correct device location. The image of the patient's anatomy may be generated either prior to or during the medical or surgical procedure. Moreover, any suitable medical imaging technique, such as X-ray, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), ultrasound, endoscopy, and optical imaging in the UV, visible, and infrared light spectrums may be utilized. For example, navigation may involve taking X-ray projections at different angular positions of a C-arm gantry and subsequent tomographic image reconstruction. With certain techniques, navigation occurs on three-dimensional (3D) images reconstructed from such X-ray projections, shortly before or during the surgical procedure.
To accurately depict the device position and orientation in the coordinate system associated with the reconstructed image, the coordinates associated with the device being employed should be correlated with the reconstructed-image (or “world”) coordinate system. This correlation usually involves transforming the device coordinates from the device coordinate system to the world coordinate system via a transform chain that includes a number of intermediate transformations. The last transform in this chain transforms a point from a coordinate system associated with a two-dimensional array of image pixels to the world coordinate system. The coordinate system associated with the two-dimensional array of image pixels may also be referred to as the “image coordinate system.”
A particulate feature of 3D navigation systems is the ability to transform the device coordinates from the image coordinate system to the world coordinate system for different gantry positions. In some implementations, the final device coordinates for display on the reconstructed image is computed by averaging the points in the world coordinate system obtained for different gantry positions for which the transform chain is established.
As will be appreciated, image-guided navigation may be complicated by navigation error, which is perceived by the operator as the distance between the tip of the navigated device in the image and the true instrument position in the image. The technique of averaging the points in the world coordinate system for the different gantry positions should reduce the navigation error. However, there is a need for additional techniques to reduce the navigation error on the reconstructed image